• Timothy Rose

DWI Glossary of Terms

DWI cases can involve a lot of terms you don't normally come across, and some that might be used in different ways.


Breath from the deepest part of the lung.

BLOOD ALCOHOL CONCENTRATION (BAC) The percentage of alcohol in a person's blood.

BREATH ALCOHOL CONCENTRATION (BrAC) The percentage of alcohol in a person’s breath, as measured by a breath testing device.

CLUE Something that leads to the solution of a problem. Used to identify "mistakes" made during the field sobriety test.

CUE A reminder or prompting as a signal to do something. A suggestion or a hint.

DIVIDED ATTENTION Concentrating on more than one thing at a time.

DIVIDED ATTENTION TEST A test which requires the subject to concentrate on both mental and physical tasks at the same time. The two psychophysical tests Walk and Turn (WAT) and One Leg Stand (OLS) require the suspect to their divide attention.

DWI/DUI The acronym "DWI" means driving while impaired and is synonymous with the acronym "DUI", driving under the influence or other acronyms used to denote impaired driving. These terms refer to any and all offenses involving the operation of vehicles by persons under the influence of alcohol and/or other drugs.

DWI DETECTION PROCESS The entire process of identifying and gathering evidence to determine whether or not a suspect should be arrested for a DWI violation. The DWI detection process has three phases: Phase One – Vehicle In Motion Phase Two – Personal Contact Phase Three – Pre -arrest Screening

EVIDENCE Any means by which some alleged fact that has been submitted to investigation may either be established or disproved. Evidence of a DWI violation may be of various types:

a. Physical (or real) evidence: something tangible, visible, or audible.

b. Well established facts (judicial notice).

c. Demonstrative evidence: demonstrations performed in the courtroom.

d. Written matter or documentation.

e. Testimony.

EXPERT WITNESS A person skilled in some art, trade, science or profession, having knowledge of matters not within the knowledge of persons of average education, learning and experience, who may assist a jury in arriving at a verdict by expressing an opinion on a state of facts shown by the evidence and based upon his or her special knowledge. (NOTE: Only the court can determine whether a witness is qualified to testify as an expert.)

FIELD SOBRIETY TEST Any one of several roadside tests that can be used to determine whether a subject is impaired.

GAIT ATAXIA An unsteady, staggering gait (walk) in which walking is uncoordinated and appears to be “not ordered.”

HORIZONTAL GAZE NYSTAGMUS (HGN) Involuntary jerking of the eyes occurring as the eyes gaze to the side. The first test administered in the SFST battery.

NYSTAGMUS An involuntary jerking of the eyes.

ONE LEG STAND (OLS) A divided attention field sobriety test. One of the tests administered in the SFST battery.

PER SE Used to describe a law which makes it illegal to drive while having a certain percentage of alcohol in the blood or breath.

PERSONAL CONTACT The second phase in the DWI detection process. In this phase the officer observes and interviews the driver face to face; determines whether to ask the driver to step from the vehicle; and observes the driver's exit and walk from the vehicle.

PRE-ARREST SCREENING The third phase in the DWI detection process. In this phase the officer administers field sobriety tests to determine whether there is probable cause to arrest the driver for DWI. Depending on agency policy, the officer may administer or could arrange to have a preliminary breath test conducted.

PRELIMINARY BREATH TEST (PBT) A pre-arrest breath test administered during investigation of a possible DWI violator to obtain an indication of the person's blood alcohol concentration.

PROBABLE CAUSE It is more than mere suspicion; facts and circumstances within the officer’s knowledge, and of which he or she has reasonably trustworthy information, are sufficient to warrant a person of reasonable caution to believe that an offense has been or is being committed.

PSYCHOPHYSICAL "Mind/Body." Used to describe field sobriety tests that measure a person's ability to perform both mental and physical tasks.

PSYCHOPHYSICAL TESTS Methods of investigating the mental (psycho-) and physical characteristics of a person suspected of alcohol or drug impairment. Most psychophysical tests employ the concept of divided attention to assess a suspect's impairment.

REASONABLE SUSPICION Less than probable cause but more than mere suspicion; exists when an officer, in light of his or her training and experience, reasonably believes and can articulate that criminal activity is taking, has taken or is about to take place.

RESTING NYSTAGMUS Jerking of the eyes as they look straight ahead.

STANDARDIZED FIELD SOBRIETY TEST BATTERY Standardized Field Sobriety Testing. There are three SFSTs, namely Horizontal Gaze Nystagmus (HGN), Walk and Turn, and One Leg Stand. Based on a series of controlled laboratory studies, scientifically validated clues of alcohol impairment have been identified for each of these three tests. They are the only Standardized Field Sobriety Tests for which validated clues have been identified

TIDAL BREATH Breath from the upper part of the lungs and mouth.

TRAFFIC SAFETY RESOURCE PROSECUTOR (TSRP) Is usually a current or former prosecutor who provides training, education and technical support to traffic crimes prosecutors and law enforcement agencies throughout their state. (For the contact information of your TSRP, contact your Highway Safety Office).

VALID Conforming to accepted principles. Producing accurate and reliable results.

VALIDATED A documented act of demonstrating that a procedure, process, and/or activity will consistently lead to accurate and reliable results.

VEHICLE IN MOTION The first phase in the DWI detection process. In this phase the officer observes the vehicle in operation, determines whether to stop the vehicle, and observes the stopping sequence.

VERTICAL GAZE NYSTAGMUS An involuntary jerking of the eyes (up and down) which occurs when the eyes gaze upward at maximum elevation. The jerking should be distinct and sustained.

WALK AND TURN (WAT) A divided attention field sobriety test. One of the tests administered in SFST battery.

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